Human blood vessels often become partly or fully occluded by various undesired materials including plaque, thrombi or other substances that restrict the flow of blood within the vessel. Depending on the location of the occlusion, serious injury or even death can occur. When diagnosed, it is often advantageous to remove the occlusive material in a safe and effective manner. Coronary heart disease is an extremely common form of this occlusive disease, and is the leading cause of death in the United States.
Arteriosclerosis is a chronic disease characterized by abnormal thickening and hardening of the arterial walls. As the coronary arteries are first narrowed by plaque, at locations known as stenoses, further constriction may be caused by the formation of blood clots, or thrombi, on the rough surface of the plaque. A severe complication of arteriosclerosis is a myocardial infarction, or MI. An MI is the death of a section of heart muscle when its blood supply is cut off, usually by a blood clot in a coronary artery narrowed by arteriosclerosis. An MI can occur spontaneously due to severely narrowed vasculature or due to an embolus, such as a thrombus released from an upstream stenosis. An embolus can even be caused in a medical procedure intended to reduce or remove a stenosis.
Various types of interventional techniques have been developed that can be utilized to reduce or remove a blockage in a blood vessel. One technique, known as balloon angioplasty, involves using a special catheter that includes a balloon near its distal tip, advancing the balloon into the constricted area, and inflating the balloon to expand the constriction. Other therapeutic options include atherectomy, deployment of stents, infusion of therapeutic medications and heart bypass surgery. All of these therapeutic options involve the risk of dislodging a portion of the occlusive material, causing embolus to move downstream thus causing further complications.
Heart bypass surgery is an extremely invasive and traumatic form of therapy to treat coronary occlusive disease. In one form of bypass, a portion of vein taken from the patient's leg, the saphenous vein, is connected between the aorta and a portion of the blocked artery distal to the blockage, supplying oxygenated blood to the portions of heart muscle supplied by the artery prior to its being occluded. These saphenous vein grafts often used in heart bypass procedures are also susceptible to occlusive disease, and over time may become restricted by plaque and thrombus. Atherosclerotic plaque in saphenous vein grafts tends to be softer and more friable than their arterial counterparts and thus more prone to embolizing during treatment.
Chemical thrombolytic drugs are available to treat saphenous vein grafts but require the patient to be non-ambulatory throughout their use and have numerous risks and complications. Balloon angioplasty of saphenous vein grafts is associated with a higher rate of embolus generation, potentially migrating downstream to block a portion of the coronary artery to which it is attached and causing a myocardial infarction. Directional Coronary Atherectomy, or DCA catheters include cutting blades that can damage the vessel wall and the systems have a propensity to become clogged and generate embolus similar to balloon angioplasty. Adjunctive devices are available to reduce the complications of embolization by trapping the released emboli downstream. These devices are expensive, and complicated to use. Vacuum extraction catheters have been developed to treat saphenous vein grafts, however they tend to be large and bulky and have had sub optimal results and numerous complications.
Clearly, therefore, there is a need for improved devices, systems and methods for removal of undesired material from an internal body conduit such as a saphenous vein graft or coronary artery that improve the efficiency of material removal and reduce the risks to the patient.